The study provides evidence that covid-19 is a seasonal infection.

A new study led by Barcelona Institute of Global Health (ISGlobal), a center sponsored by the la Caixa Foundation, provides solid evidence that covid-19 is a seasonal infection associated with temperature and moisture low, similar to seasonal flu. The results, published in Nature Computational Science, also highlight the considerable contribution of transmission by aerosol sprays and the need to adopt measures that promote air hygiene.

A key question about SARS-CoV-2 is whether he is behaving or will he behave like a seasonal virus similar to the flu virus, or if it will spread with the same intensity throughout the year.

A first study with theoretical models suggested that climate was not an important factor, given the large number of susceptible people without prior immunity to the virus. However, some observations indicated that the initial spread of the virus in China occurred at the latitude between 30th and 50th.^or N, with low levels of humidity and temperature (between 5^or and 11^orÇ).

Implementation of effective interventions

“The question of whether covid-19 is a truly seasonal disease becomes increasingly important, with implications for the implementation of effective interventions,” he explains. Xavier Rodó, director of ISGlobal’s Climate and Health Program and study coordinator.

To answer this question, he and his team first analyzed the association of temperature and humidity in the initial phase of the spread of the virus in 162 countries of the five continents, before the implementation of changes in behavior and public health policies. The results show a negative correlation between transmission rate (Ro) and global temperature and humidity: higher transmission rates were associated with lower temperatures and humidity.

Second, the researchers looked at the evolution of this association between climate and disease over time and whether it was consistent across geographic scales.

To this end they used a statistical method that was specifically designed to identify variation patterns (ie a pattern recognition tool) in different time windows. Again, they found a strong negative association for small time windows between the number of cases and climate (temperature and humidity), with consistent patterns during the first, second and third waves of the pandemic and at different spatial scales: globally, by country , by regions in heavily affected countries (Lombardy, Thüringen, Catalonia), and even at the city level (Barcelona).

Pandemic waves vs temperature and humidity

The first pandemic waves decreased with increasing temperature and humidity, and the second wave increased with decreasing temperature and humidity. However, this pattern was broken over the summer, on all continents. “This could be due to several factors, including a large concentration of young people, tourism and air conditioning, among others”, he explains. Alejandro Fontal, ISGlobal researcher and first author of the study.

When the model was adapted to analyze transient correlations at all scales in countries in the southern hemisphere, where the virus arrived later, the same negative correlation was observed. Weather effects were most evident at temperatures between 12^or and 18^orC and moisture levels between 4 and 12 g / m³, although the research team cautions that these are indicative ranges, due to the limited time of registrations.

All of our results support the idea that covid-19 is a truly seasonal infection, similar to influenza and other common cold coronaviruses.

Xavier Rodó, study coordinator

Finally, using a epidemiological model, the study shows that incorporating temperature into the transmission rate works best to predict the rise and fall of different waves, particularly the first and third in Europe. “The set of our results supports the idea that covid-19 is a truly seasonal infection, similar to the flu and other common cold coronaviruses,” says Rodó.

Seasonality can significantly contribute to the transmission of SARS-CoV-2, as low humidity conditions reduce the size of aerosols and therefore increase the airborne seasonal virus transmission like the flu.

“This association justifies emphasizing air hygiene“ through better ventilation of internal spaces, since aerosols can stay suspended for longer,” says Rodó, who highlights the need for inclusion meteorological parameters in planning and evaluating control measures.

Source: ISGlobal

Rights: Creative Commons.